Vector3D.Cross C# (CSharp) Method

    public static Vector3D Cross(Vector3D lhs, Vector3D rhs)
    {
        return new Vector3D (lhs.y * rhs.z - lhs.z * rhs.y, lhs.z * rhs.x - lhs.x * rhs.z, lhs.x * rhs.y - lhs.y * rhs.x);
    }

		/// <summary>
		/// Calculates the angle subtended by two line segments that meet at a vertex.
		/// </summary>
		/// <param name="start">The end of one of the line segments.</param>
		/// <param name="vertex">The vertex of the angle formed by the two line segments.</param>
		/// <param name="end">The end of the other line segment.</param>
		/// <returns>The angle subtended by the two line segments in degrees.</returns>
		public static double SubtendedAngle(PointF start, PointF vertex, PointF end)
		{
			Vector3D vertexPositionVector = new Vector3D(vertex.X, vertex.Y, 0);
			Vector3D a = new Vector3D(start.X, start.Y, 0) - vertexPositionVector;
			Vector3D b = new Vector3D(end.X, end.Y, 0) - vertexPositionVector;

			float dotProduct = a.Dot(b);

			Vector3D crossProduct = a.Cross(b);

			float magA = a.Magnitude;
			float magB = b.Magnitude;

			if (FloatComparer.AreEqual(magA, 0F) || FloatComparer.AreEqual(magB, 0F))
				return 0;

			double cosTheta = dotProduct/magA/magB;

			// Make sure cosTheta is within bounds so we don't
			// get any errors when we take the acos.
			if (cosTheta > 1.0f)
				cosTheta = 1.0f;

			if (cosTheta < -1.0f)
				cosTheta = -1.0f;

			double theta = Math.Acos(cosTheta)*(crossProduct.Z == 0 ? 1 : -Math.Sign(crossProduct.Z));
			double thetaInDegrees = theta/Math.PI*180;

			return thetaInDegrees;
		}